The invention concerns a process and equipment for the separation of the tar and ammonia liquor mixture from coke oven plants. The coarse components are conventionally separated in a primary separator or decanter and, by utilizing heat, such as heat of the separated ammonia liquor, continuously divided into tar and ammonia liquor.
Devices and equipment for separating tar from ammonia liquor are known, for instance, in German Patentschrifts Nos. 917,388 and 935,020 as well as Auslegeschrift No. 1,057,721. The tar collecting tank of the tar separator has a lower tapered portion, and is enclosed by the ammonia liquor storage tank. The tar discharge pipe can be installed deep in the inner part of the tar collecting tank.
Other separating devices for tar and ammonia liquor are designed according to similar principles, for instance the equipment according to German Auslegeschrift No. 1,044,342 and Patentschrift No. 1,156,823, of which the latter is said to operate without prior separation of the heavy tar.
If necessary, and for special requirements regarding the purity of the tar, such as solids and water content two tar separators can be connected in series as shown in German Offenlegungschrift No. 2,257,428. Also, temperatures above 100.degree. C. and increased pressures have been applied for the separation (German Patentschrift No. 1,020,349).
These known devices are provided for coke oven plants in which a coal with a water content of 5-10% is charged into the ovens. Where this type of coal is not finely ground, the separation into a tar and liquor phase with known technology is adequate.
The gas which is emitted during the manufacture of coke contains typically about 30% of the weight of the coal in the form of organic "volatiles" as well as considerable moisture. This gas is usually sprayed with water or with recycled "flushing liquor" to remove entrained solids, generally in the form of tar. The collecting main for the gas passes the whole length of the battery, each lead-in having a spray and additional sprays being spaced about every third oven. A suction main tied in to the collecting main will ordinarily contain about 25% by volume of a mixture of tar and "liquor". The liquor containing the tar is taken to a decanter, where it is allowed to separate into tar on the bottom and an aqueous ammonia liquor which may be decanted off. A portion of the aqueous liquor may be recycled for use in the sprays as described above.
The reader may also be interested in reviewing U.S. Pat. Nos. 2,018,377, 2,697,067, 2,775,541, 2,799,678, and 2,937,130.
Recently the art has begun to use very finely ground and pre-dried coals or preheated coals, having very low moisture contents in order to obtain faster coking rates and to increase the throughput capacity of the oven battery. It has been found that the known systems and processes for the separation of the tar and ammonia liquor mixture are not sufficient for use with finely ground, preheated systems, because the clean separation necessary for a trouble-free operation could not be attained. Generally using prior art systems, the moisture content of the tar is too high so that it can frequently be useless. Also, the tar content of the liquor phase cannot be tolerated because when returning the ammonia liquor to the collection main of the battery, the spraying nozzle becomes fouled and the surplus liquor deposits its tar content in the treatment plants.
The condensates in the tar and ammonia liquor produced when charging finely ground pre-dried or preheated coal into the oven chambers tends to form suspensions and foam which cannot be separated properly in known devices and according to known processes, because they have a persistent stability which is detrimental to the operation. This tendency to form suspensions and foam is favored by the presence of finely dispersed solids, particularly coal particles which are coated with tar and which float in the ammonia liquor and form, with the addition of air and other gases, a floating disperse system, or foam. Surfactants appear to be formed, especially in the presence of ammonium and chloride ions, wnich can promote the formation of suspensions and foam.
A further separation of foam and suspension has been used by the liquid streams leaving the tar separators sometimes under pressure, heated and/or with the addition of the salts of multi-valued acids which have a separating effect on colloidal systems. In such cases additional expenditures for apparatus and considerable additional expenses for energy and chemicals are necessary.